Evaluation of usage of plasma torches in cement production
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Sustainable energy systems (MPSES), MSc
Publicerad
2019
Författare
Burman, Tove
Engvall, Johanna
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This work developed and evaluated a heat transfer model for the cement production process, focusing on the rotary kiln but also including the cyclone tower. The purpose of the model is to evaluate the implementation of new heat sources, in this case plasma torches. The rotary kiln model is discretised in angular, axial and radial directions and describes the heat transfer characteristics of the gas, walls, and material in the kiln. The heat transfer includes a description of the radiation, convection, and conduction between the cells. The model also includes the flow of gas and material as well as the mixing within the bed due to the rotation of the kiln. The heat transfer in the cyclone tower is assumed efficient and the units are described by simple heat and mass balances. The model is validated against two distinctive cases of operational conditions of production line 8 at Cementa in Slite. An important part of the work was to define and collect data for the model validation. The model shows good agreement with the measured wall temperatures, considering the outside cooling is not included in the model. The results, such as product temperature and heat absorbed by the bed, are consistent with gathered data using a reasonable gas temperature profile and found equilibrium data. The requirements of the material to reach the desired quality is key to the process and emphasis is put on how to incorporate these requirements into the heat transfer model. The work concluded that a detailed description of the reaction kinetics and heat of reaction is difficult to include in the model due to its complexity and the maturity of the field. Instead this work recommends that seven heating zones are defined through the kiln where the required residence time and heat is determined externally by experiments or detailed modelling of the cement chemistry. In this way the heat transfer model and bed model could in concert and in an iterative manner decide the required temperature profiles and conditions (e.g. gas concentrations or particle loads) of the gas as well as the dimensions of the kiln to achieve the desired product temperature. The model was applied to evaluate the implementation of a plasma torch in the cement kiln. Compared to today’s combustion of coal and other fuels, the plasma torch will decrease the particle load and change the gas composition. The result shows that significantly (400°C) higher gas temperatures are required in the kiln with plasma torch operation, to reach the desired bed temperatures. Furthermore, the example highlights the importance of being able the predict the development of the gas temperature profile through the kiln. Here the work recommend future work with measuring or detailed modelling (CFD) of the gas phase temperature.
Beskrivning
Ämne/nyckelord
Energiteknik , Hållbar utveckling , Energi , Energy Engineering , Sustainable Development , Energy